Various types of inking systems for printing machines use troughs in which a doctor blade can be adjusted in longitudinal position with respect to the gap or nip between the blade and the inking trough. Usually, adjustment screws are provided, set along the length of the doctor blade in the inking system, and engaging the doctor blade so that the doctor blade can be pressed against the duct roller at various locations, independently of the position of the blade with respect to adjacent locations, so that the thickness of the ink film picked up by the duct roller can be adjusted in zones extending axially across the duct roller (see, for example, German Pat. No. 863,346). In some arrangements of this type, a double-armed lever is positioned between the adjustment screws and control rods engaging, or coupled to, the doctor blades. The various levers are engaged by cams which are positioned on a shaft common to the levers and which can be rotated by a hand crank or the like.
It has been found that ink systems of this type are subject to contamination by ink which penetrates between the doctor blade and the backing plate or ink bottom plate of the ink trough. Such ink which penetrates or drips into that gap causes the mechanism to gum and may lead to malfunction and, in limiting cases, to inoperability.
It has already been proposed--see U.S. Pat. No. 1,825,999--to prevent escape of ink between the backing plate and the doctor by the specific construction of the trough system. The various elements to control the nip between the doctor blade and the duct roller are located beneath the duct roller. If ink is used which is comparatively liquid, ink dropping off the duct roller may contaminate the adjustment elements located therebeneath. Such ink which in the course of time will accumulate and dry can interfere with proper operation of the adjustment mechanism.